Inverse CO 2 /C 2 H 2 Separation with MFU-4 and Selectivity Reversal via Postsynthetic Ligand Exchange.

Although many porous materials, including metal-organic frameworks (MOFs), have been reported to selectively adsorb C 2 H 2 in C 2 H 2 /CO 2 separation processes, CO 2 -selective sorbents are much less common. Here, we report the remarkable performance of MFU-4 (Zn 5 Cl 4 (bbta) 3 , bbta=benzo-1,2,4,5-bistriazolate) toward inverse CO 2 /C 2 H 2 separation. The MOF facilitates kinetic separation of CO 2 from C 2 H 2 , enabling the generation of high purity C 2 H 2 (>98 %) with good productivity in dynamic breakthrough experiments. Adsorption kinetics measurements and computational studies show C 2 H 2 is excluded from MFU-4 by narrow pore windows formed by Zn-Cl groups. Postsynthetic F - /Cl - ligand exchange was used to synthesize an analogue (MFU-4-F) with expanded pore apertures, resulting in equilibrium C 2 H 2 /CO 2 separation with reversed selectivity compared to MFU-4. MFU-4-F also exhibits a remarkably high C 2 H 2 adsorption capacity (6.7 mmol g -1 ), allowing fuel grade C 2 H 2 (98 % purity) to be harvested from C 2 H 2 /CO 2 mixtures by room temperature desorption.